R. Thomas Zoeller uses an iPhone application that flags products with potentially dangerous chemicals to help him make wise choices at the grocery store.

Dr. Perry E. Sheffield washes her hands often — as much to get rid of potentially dangerous chemicals as germs.

It’s nearly impossible to prove scientifically that certain diseases are caused by household chemicals, such as bisphenol-A, phthalates, and flame retardants, which are found in everything from kitchen cleaners to baby creams, carpeting to tin cans.

But as research accumulates about their potential dangers, and rates of diseases that are plausibly caused by these chemicals rise, these three scientists are anxious enough to make changes in their own homes.

“Effectively, we’re conducting experiments on our population,’’ said Sheffield, an assistant professor of preventive medicine and pediatrics at Mount Sinai School of Medicine in New York.

Researchers long ago proved that chemicals like bisphenol-A and phthalates can disrupt development in animals by interfering with their hormones. Now, scientists are increasingly demonstrating that these chemicals, known as endocrine disruptors, might be harmful to people, too.

“What’s happening to rats and mice is an indicator of what’s happening to humans,’’ said Soto, professor of cellular biology at Tufts University School of Medicine.

In one study of 427 men published in December, those who had the most bisphenol-A — known commonly as BPA — in their urine reported the highest levels of sexual problems, from decreased desire to lower satisfaction with their sex lives. In a 2009 study of 250 toddlers, girls (but not boys) were more likely to act aggressively if their mothers had high urine levels of BPA during pregnancy.

And a national survey of more than 1,400 adults showed that people with higher concentrations of BPA in their urine were more likely to have been diagnosed with heart disease or diabetes, according to a 2008 study in the Journal of the American Medical Association.

None of these studies are conclusive evidence of harm, the researchers said, because they do not meet the gold standard of medical research. To do that, scientists would have to study two large populations of people — one exposed to a chemical and one not — potentially for decades, to see if there are health differences between the two. Since virtually everyone is exposed to the major chemicals, and since our lifestyles differ in so many different ways, it would be nearly impossible to conduct such a study. Instead, researchers look to animal studies and weaker human studies to build a case.

The scientists interviewed for this story said enough data has accumulated to suggest that these chemicals might be harmful — and that we should take precautions as if they were.

It’s scientifically plausible that these chemicals account for some cases of autism, ADHD, learning disorders, and autoimmune problems like allergies and asthma, said Zoeller, a biology professor at the University of Massachusetts-Amherst and chairman of the Environmental Protection Agency’s Exposure and Human Health Committee.

The question is how much exposure is too much.

Chemical safety consultant Neal Langerman said the general public has nothing to fear from the low concentrations of these chemicals in household products. “BPA is an endocrine disruptor. That’s a hazard. No one’s going to argue with that,’’ said Langerman, offered as a spokesman by the American Chemical Society, a 163,000-member scientific organization of chemists and chemical engineers. “[But] BPA as it appears in consumables is at such low concentration’’ that there is very little risk from using products containing it, he said.

Virtually all of us are exposed to these chemicals, which can break free of the products they are embedded in and become airborne or dissolved in liquids or food. Research by the US Centers for Disease Control and Prevention shows that 93 percent of Americans over age 6 have BPA in their bodies. Almost the same percentage of Canadians are exposed — but Americans have higher levels, with two-times more BPA in their urine than Canadians, according to a study published last week and led by Laura N. Vandenberg at the Center for Regenerative and Developmental Biology at Tufts University.

Exposures are cumulative, so one swig of tea warmed in a plastic cup containing BPA doesn’t pose a danger — the body clears a single exposure to BPA within days. But a lifetime of re-exposing yourself by repeatedly drinking small amounts of BPA with your morning tea might cause problems.

The trouble is no one knows how much each exposure matters.

And no one knows how the chemicals might interact with each other, compounding their impact on the body.

No one knows in part because chemical companies aren’t required to find out.

Toxicity studies on new chemicals are not required unless the compounds will be used in drugs, pesticides, or food. There’s actually a disincentive for companies to study the potential health effects of new chemicals, according to Carl F. Cranor, a University of California-Riverside professor and author of a new book, “Legally Poisoned: How the Law Puts Us at Risk From Toxicants’’ (Harvard University Press). If a company studies a chemical, it must tell the EPA what it finds; if it doesn’t study the chemical, there’s no chance it will find something bad, he said.

Taking steps at home to reduce exposure is a good idea, researchers said — but it’s not enough.

“You should do it because it’s the only tool you have today,’’ Soto said. “But you should ask for better tools.’’

All the researchers contacted for this story said congressional action is needed to strengthen testing of chemicals before they reach everyday products.

Massachusetts US Representative Edward Markey, a Malden Democrat, introduced legislation last month to ban BPA from all food and beverage containers.

Langerman thinks such legislation is a bad idea.

The market is a better regulator than politicians, said Langerman. Historically, he said, court decisions create change faster and more effectively than Congress. Companies will find healthier alternatives themselves, he said, when they are available and inexpensive — and when pressured by customers.

Philips Electronics, for instance, took BPA out of its Avent baby bottles in 2008 after a public outcry from parents who didn’t realize the chemical was in the bottles. Philips is also involved in a class action legal settlement, offering to reimburse the cost of bottles purchased since Jan. 1, 2001. (For more information, go to www.philipsbpasettlement.com/?gclid=COO35Y7vgKcCFcbd4AodDj2-fA.)

Out of an abundance of caution, Langerman agrees that pregnant women should limit exposure to BPA and that baby bottles should be BPA-free. As for himself, Langerman said he’s going to keep drinking out of plastic water bottles.

“When you look at BPA, the facts just aren’t there. Should we act to protect ultrasensitive populations? Yeah, but parents can do that themselves,’’ he said.

Pregnancy and early childhood are particularly vulnerable times, research shows, with toxins especially destructive while infant brains and immune systems are developing. A study from the University of Rochester found that boys born with high levels of phthalates in their urine were more likely to show signs of reproductive problems.

Adults may be vulnerable, too. Soto says that the experience of women given DES during pregnancy shows that endocrine disruptors can cause cancer in people. Women who were given DES, a synthetic form of the hormone estrogen, have a slightly elevated risk of developing breast cancer, and their daughters also run a higher risk of breast, cervical, and vaginal cancers, according to the National Cancer Institute.

Endocrine disruptors affect men, too. A 2010 study of 50 men at a Boston infertility clinic showed that they were more likely to have a low sperm count if the dust in their home contained high levels of flame retardants.

And a 2008 study of farm workers in California’s Central Valley showed the men and women had a significantly higher risk of developing Parkinson’s disease if they were exposed to two particular pesticides.

So, why aren’t we all sick?

The human body is naturally resilient, Zoeller said, and eating well, exercising, and being generally healthy can help it cope with the extra chemicals. That may be why most of us don’t seem bothered by the potential toxins in our water bottles, homes, and diet. At least not yet.